Order VIII.—Rodentia[24] (gnawing animals). Animals of this order have two large, chisel-like incisors in each jaw, and, separated from them by a wide space, are the molar teeth. The incisors never cease growing from the roots, but are constantly worn away by nibbling. The lower jaw moves backward and forward. This order includes more than half of the known mammals, and its representatives range from the equator to the poles. Hares, Mice, Rats, Squirrels, and Beavers are among those best known.
Order IX.—Ungulata[25] (hoofed animals). An order of mammals most valuable to man. They are grouped in two divisions, according to the number of toes. The uneven-toed ungulates include the Elephant, Rhinoceros and Horse. The elephant is marked by the prolongation of the nose and upper lip into a trunk or proboscis, which is said to contain over 40,000 muscles. It has no canine teeth, and incisors only in the lower jaw. Elephants are found in Asia and Africa. There are two extinct species, the mastodon and mammoth. The rhinoceros is a native of Africa and India. It is an immense animal, covered by a hairless skin, which lies in folds on the body. The nose bears one or two horns, which grow sometimes three feet in length. The horse includes animals having one toe upon each foot, upon which they walk. The family includes the Ass, Zebra and Quagga.
The even-toed ungulates include all the Ruminates, or cud chewing animals, with the Swine and Hippopotamus. The ruminants are remarkable for their peculiar method of digesting their food. They possess a very peculiar stomach, of four compartments. The food, mixed with saliva, is swallowed and passes into a paunch where it is mingled with water, and then forced into what is called the honey-comb stomach, a sack in which the food is formed into cuds, and by a muscular arrangement is forced back into the mouth to be masticated a second time before passing directly into the third stomach or manyplies, where it is strained, and then driven into the true stomach to be acted upon by the gastric juice and assimilated.
The deer is a fine representative of the ruminant, with solid branching horns. Like all ruminants it has two toes. There is a large class of cud-chewers having hollow horns, which usually are not shed, as are the solid horns. The Buffalo, Ox, Sheep, Goat and Antelope belong to this division.
OX SKELETON.
10, horns; 8, spine; A, cervical, B B, dorsal, C, lumbar, D, sacral, and E E caudal vertebræ; F F, ribs; G, sternum and cartilages; R, ossa innominata; H, scapula; I, humerus; K, radius; L, ulna; N, metacarpal; S, femur; T, patella; U, tibia; V, hock; X, metatarsal; Y, small metatarsal; P, sesamoids; Y, bones of tarsus, nine in number. Figures near Z: 1, infero maxilla; 2, supero maxilla; 3, premaxilla; 4, nasal; 5, lachrymal; 6, frontal. Figures near letter M, bones of the carpus or knee, 1, trapezium; 2, cuniform; 3, lunar; 4, scaphoid; 5, unciform; 6, magnum. Figures near the letter Q, mark the three phalanges, or small bones of the foot.
The Giraffe, an inhabitant of Central Africa, and remarkable for its long neck, is another ruminant. The camel also belongs here. The true camel has two fatty humps upon its back; another species, called the dromedary, has but a single hump. The camel has a peculiar modification of one compartment of the ruminant stomach. The paunch is divided into cells which hold supplies of water.
Order X.—Carnivora (flesh-eaters). The distinguishing characteristics of this order are sharp canine teeth, and one molar on each side in the upper and lower jaw, longer and sharper than the rest; and feet which are provided with toes, generally supplied with claws. According to the modifications of the feet they are divided into Pinnigrades, Plantigrades and Digitigrades. The first have short, webbed feet which they use as paddles for swimming, and are represented by Seals and Walruses. These are amphibious mammals of a high order. They spend much of their time in the water, and both the form and covering of their bodies are adapted to their aquatic mode of life. They swim and dive with the greatest facility. The soft woolly down, close to the skin, is covered with a coat of long, smooth, shining hairs which lie close to the body, offering no resistance to their passage through the water. Their skins and oil are of considerable mercantile importance. The Plantigrades include those animals which in walking place the sole of the foot flat upon the ground. Such are Bears and Raccoons. The Digitigrades are those which walk on the toes, as Weasels, Foxes, Dogs, Cats, Lions and Tigers.
Order XI.—Primates are at the head of the animal kingdom. The distinguishing characteristics of this class are the more erect carriage of the body, a hand better adapted for use, its fingers being furnished with nails, and a thigh free from the body. The order includes the Lemurs, Monkeys, Apes and Man. The lowest division of the primates, the lemurs, are small animals whose bodies are covered with hair. They have a fox-like face, a pointed nose, large ears, and a long tail, and they walk on all fours. The monkeys have long prehensile tails, and though their hands can be used for grasping, the thumbs are not opposable. A distinguishing mark is the number of teeth; they have thirty-six instead of thirty-two, as the apes and man. Among the monkeys are the Baboon, the Howling Monkeys, the Mandril, and the Sleepers of Africa and Asia.